Dear Liz,

    Thank you very much ____ your letter and the photos of your ____ (friend) and family. Your parents and friends look really nice ____ the photo. Now I can tell you something about me and ____ (I) family here in New York.

    I've got two brothers. ____ (they) names are Lukas and Andreas and they ____ (be) 16 and 19. My mother is French and her name is Christine. Dad is American and his name's Dieter. Our house ____ (have) got four bedrooms and a small garden. My room is tidy, but my ____ (brother) is not. They don't often clean it. We have a dog, Zak, and we think he's cute. We ____ (love) it a lot.

    Please tell me all about ____ (you) friends and school in your next letter. I'd like to know about English schools.

Love,

Laura

某科学兴趣小组的同学在老师的指导下，正确完成如图所示两个实验。已知所用实验装置气密性良好。

关于该实验，有如下说法：

①红磷熄灭并冷却后才能打开弹簧夹；

②点燃酒精灯加热铜丝，可观察到铜丝由红色变成黑色；

③停止加热后即可读出注射器内气体的体积约为24mL；

④实验取用铜丝质量的多少不会影响实验结果；

⑤两个实验均能证明空气是混合物；

⑥两个实验均能证明空气中约含1/5体积的氧气.

其中正确说法的个数有（  ）